A father and son look at the space shuttle orbiter Discovery on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. Shuttle Discovery had 27 years of service and flew 39 times before being retired in 2011. (Photo by Gary Cameron/Reuters)

A tour group gathers under a Lockheed SR-71 Blackbird at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. The SR-71 was a long-range spy plane that was in use from 1964 to 1998 and designed to operate at three times the speed of sound. (Photo by Gary Cameron/Reuters)

Tourists are dwarfed by the space shuttle orbiter Discovery on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A man photographs the main engines of the space shuttle orbiter Discovery on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A Lockheed SR-71 Blackbird is seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

Tourists look at the space shuttle orbiter Discovery on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A Lockheed SR-71 Blackbird is seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A Lockheed SR-71 Blackbird is seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

The Enola Gay, a Boeing B-29 Superfortress bomber, is seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. The Enola Gay dropped the first atomic bomb in history over the city of Hiroshima in Japan 70 years ago. (Photo by Gary Cameron/Reuters)

The nose section of the Enola Gay, a Boeing B-29 Superfortress bomber, is seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A Boeing 307 Stratoliner, the first pressurized cabin passenger aircraft, is seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A Boeing 307 Stratoliner, the first pressurized cabin passenger aircraft, and an Air France Concorde supersonic airliner, are seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

The nose cone (R) and thermal tiles (L) of the space shuttle orbiter Discovery are seen on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A replica of the Wright Brothers Model B aircraft is seen on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A Boeing 367-80 (prototype to the Boeing 707) (front), a Boeing 307 Stratoliner (rear, R), the first pressurized cabin passenger aircraft, and an Air France Concorde supersonic airliner (rear, C) are seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

Satellites and space probes hang on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A Curtis P-40 Flying Tiger WWII vintage fighter aircraft is seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

Satellites and space probes hang on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

World War Two vintage Curtis P-40 Flying Tiger (L) and a Vought F4U-1D Corsair (R) aircraft are seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

The fuselage of the space shuttle orbiter Discovery is seen on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

The fuselage of the space shuttle orbiter Discovery is seen on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

The space shuttle orbiter Discovery (R) is seen on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A lunar dust brush used for Apollo mission training is seen on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A Globe Swift two-seat aircraft is seen on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

The fuselage, and heat tiles (bottom), under the wing of the space shuttle orbiter Discovery are seen on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

The main engines of the space shuttle orbiter Discovery are seen on display at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)

A Lockheed SR-71 Blackbird is seen at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. (Photo by Gary Cameron/Reuters)